Down draft carburetor



Dec. 29, 1931. H w. LINKERT DOWN DRAFT CARBURETOR Filed July 11,

1929 2 Sheets-Sheet III jllllllllllllllll z ,1

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H. w. LINKERT 1,838,421

DOWN DRAFT CARBURETOR Filed July 1, 1929 2 SheetsSheet 2 (EVEN; :1

Patented ea. 29, 1931 UNITED STATES PATENT OFFICE HOWARD W. LINKERT, OFINDIANAPOLIS, INDIANA, ASSIGNOR TO THE WHEELER- SCHIEBLER GARBURETORCOMIANY, OF INDIANAPOLIS, INDIANA, A CORPORATION OF INDIANA DOWN imar'rcnnsunn'ron.

Application filed July 11, 1929. Serial No. 377,354.

This invention relates to down draft carburetors for internal combustionengines.

It is an object of this invention to provide a down draft carburetor ofthe air valve type that will provide a'le'an and economical mixture fora wide range of normal operating conditions, While having a richermixture range for developing full power,'together.

with means for enriching the mixture to assist in starting a coldengine. In order to provide a satisfactory lean and economical mixturefor normal operating conditions, I provide a metered fuel supply to adownwardly opening nozzle together with an air bleed well into the fuelline between the metering orifice and the nozzle to assist in atomizingthe fuel before it issues from the nozzle. The conventional up-draftcarburetor and manifold allows fuel to collect on the riser andcarburetor walls at low air velocities causing loading and lag uponacceleratin. Thus, an up-draft carburetor is limited in size of airpassages and riser diameter by the permissible value of the low airvelocity.

If too large a carburetor is used undue body loading results at'low airvelocities with consequent trouble in Working out satisfactoraccelerating properties. In a down-dra carburetorv of the type of thisinvention no fuel can collect in disturbing quantities in the carburetoror the connecting tube to the manifold runners so that the carburetorand connecting tube will not load up, even with an enlarged carburetor.Thus, larger air passages and venturis may be used in the carburetorofvthis invention to increase the maximum speed and power output of theengine without decreasing the idling and accelerating performancethereof.

It is also an object of this invention to pro videa simplified andimproved down draft carburetor wherein an efiicient automatic control ofthe fuel and air mixture ratio Wlll.

be maintained under varying operating conditions.

Other and further important objects of this inventionwill be apparentfrom the disclosures in the specification and the accompanying drawings.

This invention (in a preferred form) is illustrated in the drawings andhereinafter more fully described.

On the drawings:

Figure 1 is a side elevation of a carburetor embodying the features ofthis invention.

Figure 2 is an enlarged longitudinal central section on a plane parallelto that of Figure 1.

Figure 3 is a vertical section on the line IIIIII of Figure 2. i 1

Figure 4 is a horizontal section on the line IVIV of Figure 2.

As shown on the drawings:

The carburetor of this invention comprises a vertically disposed mixingchamber having a flanged bottom outlet 11, for attachment to the intakemanifold, and containing the usual throttle valve 12 on a throttle shaft13, as Well as a central primary ventu-ri 14 having a separate primaryair inlet passage 15 leading thereto. The mixing chamber 10 has anauxiliary air inlet pas-. sage 16 connected thereto and having a formedauxiliary air valve seat or port 17 against which a disc type ofauxiliary air valve 18 seats at low suctions.

A'float bowl 19 is positioned beneath the auxiliary air inlet passage 16and is'provided with the usual float and lever 20 controlling a valve 21in a fuel inlet connection 22. From the float bowl fuel is drawn throughthe passageway 23past a tapered needleor fuel valve 24, and iscontrolled at I the circular orifice formed between the top of the passaeway 23 and the valve 24. It then passes t rough a drilled hole 25 intoan annular well 26 formed between a sleeve 27,

forming the passageway 23, and a vertical aperture 28 in the body 10.This Well opens at its top into the floor of the inlet passage 16,forming an air bleed into the well, the sleeve having a fluted band inthe Well 26 to center the same while admitting air therepast. From thewell 26 a passage '29 leads to a downwardly openin nozzle 30 locatedcentrally of the throat o the primary venturi 14. The fuel valve 24 hasa short cyllndrical section 31 by which it is guided 1n the orifice.

The sleeve 27 is threaded into its apert 28 and at its upper end isprovided with a worm gear 32 engaged by a worm 33 having an externalmilled head 34 to form the idling or low s eed adjustment. Turning thehead 34 will t us screw the sleeve 27 up or down in the aperture 28 thusraising or lowering the seat for the fuel valve 24 and making theinitial adjustment, and to a small extent the range, leaner or richer,respectively.

As the rate of flow of air through the carburetor is changed, the airand fuel should be kept in the proper proportions. This is done byhaving the air valve 18 controlling the amount of air entering thecarburetor, aside from the small primary air sup ly, the fuel valve 24controlling the fuel, and a proportioning lever 35 transmitting to thefuel valve a definite portion of the motion of the air valve, so that asthe air flow increases, the fuel flow also increases in the properproportion. The air valve 18 is mounted on a rod 36 extending into adash pot 37. An arm 38 is secured between the valve and the rod, whicharm is pivoted to one end of the lever 35. The leverpasses through atrunnion block 39 slidable on the lever and in turn pivotally mounted onthe end of an adjustable fulcrum arm 40. On the other end of the lever35 is another sliding block 41 pivotally attached to the top of the fuelvalve 24. Thus, as the air valve 18 moves, the proportioning lever 35turns about the pivot of the trunnion block 39 and gives to the fuelvalve a motion that is in proportion to that of the air valve.

The taper of the fuel valve and the form of the air valve seat are sochosen as to provide a substantially uniform fuel and air ratio suitablefor best economy under conditions of normal operation. However, formaximum power a richer mixture is desirable and, in order to obtain thisricher mix-, ture atv any point in the range, the fulcrum arm 40 is madead'ustable to vary the proportioning effect 0 the lever 35. The arm 40is fastened to a shaft 42 passing through the body to the outside. Aiarm 43 is fastened to this shaft on .its outer end, this arm having alost motion engagement with a rod 45 connected to a lever 46 on thethrottle shaft" in such a manner that the throttle operates the leveronly when nearing full open osition, in order .to enrichen the mixtureor full power. An arm 44 is loosely pivoted on the shaft and is providedwith a projecting lug 55- engaging the arm. A spring 56 is coiled aboutthe shaft and acts to hold thearm 43 against the lug 55 except when therod 45 pulls the arm down. A rod 47 is linked to the arm 44, forming adash enrichening control similar. in effect to a choke control. The arm43 is so arranged as to be depressed when the throttle is wide open orthe choke'c'ontrol is pulled to the right, and the trunnion block 39 isthereby larly, the dash control acts through the rod" 47 to turn thefulcrum arm 40 to shift the trunnion block towards the air valve to increase the liftof the fuel valve, and to even cause a considerable liftof such fuel valve while the air valve is on its seat, thus materiallyenrichening the mixture for starting purposes with a cold engine.

The dash pot 37 serves to keep the air valve from fluttering. The dashpot lies below the fuel level in the float chamber and is thus alwaysfull of fuel. A dash pot piston/18 is mounted on a sleeve 49 and isrovided with passages 50 therethrough which are closed by a disc 51 on ashouldered nut 52 which engages the rod 36 but allows the disc to dropaway slightly from the piston. The sleeve 49 is slidable on the airvalve rod 36, but is normally held in fixed position against the nut bya spring 53 above the sleeve. The fluctuations in the suction of theengine tending to cause the air valve to flutter, are small in magnitudeand the spring 53 is strong enough to resist them completely and forcethe piston to remain firmly in place and act as a solidly mountedpiston. When the throttle is opened after coasting a very high manifoldsuction is suddenly imposed on the air valve, causing a very strongopening pull which is sufficient to overcome the initial load on thespringv 53, thus compressing it and allowing the piston and sleeve toslide on the rod 36, allowing' the air valve to drop as though the dashpot were omitted. A spring 54, beneath the piston, acts against the nutand rod 36 to return the air valve to its closed position upon closingof the throttle.

In the operation of this down draft carburetor the engine suction drawsa primary air supply through the passage 15 and venturi 14 Where the airpicks up fuel from the nozzle 30. When the auxiliary air valve is closedthe fuel passage at the valve 24 is greatly restricted so that thesuction at the venturi draws both air and fuel from the well 26,whereas, when the air valve opens the .fuel valve opens correspondinglyso that suiiicient fuel is supplied under all conditions while the airbleed limits the suction on the fuel metering valve thus permitting theuse of an open nozzle of relatively large size. As previously described,the sleeve 27 is vertically adjustable to form the idling adjustment,While the leverage or fulcrum point is shiftable to vary the ratiobetween the fuel and air supply as the auxiliary air valve opens. Theinitial or base ratio of fuel to air is determined by the profile of theformed air valve seat 17 which is initially determined by a series ofexperime ts to give proportions offuel and air suitable or a given typeand design of engine, as it has been found desirable to fit thecarburetor to individual designs of engines to obtain the maximumpossible performance throughout the operating range.

It will thus be seen that I have provided an improved down draftcarburetor embodying a wide range of capacity with an independentcontrol of the mixture ratio at different speeds and loads with a simplesingle fuel passage or nozzle.

I am aware that many changes may be made andnumerous details ofconstruction may be varied through a wide range with out departing fromthe principles of this invention, and I therefore, do not purposelimiting the patent granted hereon, otherwise than necessitated by theprior art.

I claim as my invention:

1. A down draft carburetor comprising a downwardly discharging throttlecontrolled mixture outlet passage, an inverted primary venturipositioned therein and having its own primary air supply passage, a fuelnozzle discharging into said venturi, a fuel metering valve supplyingfuel to said nozzle, an air bleed fuel well interposedbetween saidmetering valve and said nozzle, an auxiliary air valve for admittingadditional air to said mixture outlet passage, and means interconnectingsaid auxiliary air valve and said fuel metering valve to increase thedelivery of the latter valve as the air valve opens.

2. Adown draft carburetor comprising. a downwardly discharging throttlecontrolled mixture outlet passage, an inverted primary venturipositioned therein and having its own therein, a valve for supplyingfuel to said nozzle comprising an adjustable sleeve and a valve movablein said sleeve, said sleeve being.

being so mounted as to form an open annular fuel well between said valveand said nozzle, an auxiliary air valve, mechanism connecting said airvalve to said fuel valve to proportionally vary the opening of saidvalves, and means for varying the proportioning eifect of saidmechanism.

In testimony whereof I have hereunto subscribed my name at Indianapolis,Marion County, Indiana.

HOWARD W. LINKERT.

primary air supply passage, a fuel nozzle discharging into said venturi,a fuel metering valve supplying fuel to said nozzle, an auxiliary airvalve for admitting additional air to said mixture outlet passage, ap'roportioning mechanism interconnecting said fuel and air valves tovary the delivery of the fuel valve, means for varying the proportioningeffect of said mechanism, and an air bleed fuel Well interposed betweensaid metering valve and said nozzle.

posed between said metering valve and said I nozzle.

4. A down draft carburetor com rising an inverted primary venturi havinga uel nozzle

